Saint Louis University Intro to Linux and C

Saint Louis University Intro to Linux and C CSCI 2400/ ECE 3217: Computer Architecture Instructors: David Ferry 1

Saint Louis University Overview Linux ¢ C ¢ Hello program in C ¢ Compiling ¢ 2

Saint Louis University History of Linux ¢ Way back in the day: Bell Labs Unix § Widely available to students and instructors § Very machine-independent Some direct Unix branches (e. g. Berkeley Unix or BSD) ¢ Others were inspired by Unix ¢ § Minix- by Andrew S. Tannenbaum, an educational micro kernel § Could re-implement the high-level design of Unix (e. g. Minix was originally system-call compatible with Unix) ¢ Linus Torvalds saw Minix and wanted to do his own version § § Wrote basic kernel from scratch Borrowed good ideas from Minix Included early support for GNU project software Completely free OS and system software 3

Saint Louis University Linux Today Very small usage in desktop/laptop market (~3% in US) ¢ Android is the biggest OS in mobile computing (~53% of US) ¢ § Up to 85% of devices worldwide Linux drives internet servers (~97% of public servers) ¢ Linux drives supercomputing (~99% of TOP 500 computers) ¢ 4

Saint Louis University Getting Started with Linux at SLU Linux classroom and Linux lab on 1 st floor Ritter ¢ Department Linux server: hopper. slu. edu ¢ Should use same username as SLU, but different password ¢ Talk to Dennis about password issues (office adjacent to lab) ¢ Recommended: Login to hopper. slu. edu via ssh ¢ Suggested: Work on local machine in lab ¢ Suggested: Login to hopper. slu. edu via No. Machine ¢ You may work however you like, but I can’t support other methods (e. g. Linux in a virtual machine on your laptop) ¢ 5

Saint Louis University Logging in via SSH ¢ From OSX – can use terminal directly § Can transfer files with ‘scp’ command ¢ From Windows – can use an ssh client § My favorite: Secure Shell extension for Chrome browser § Plenty of others, just search for them § Transfer files via Win. SCP Username: your SLU username ¢ Hostname: hopper. slu. edu ¢ ¢ Via terminal: ssh dferry@hopper. slu. edu 6

Saint Louis University Using the command line Enter one command per line ¢ Lots of programs to accomplish what you want to do ¢ § Just search “How do I accomplish XYZ in Linux terminal? ” ¢ Useful commands: Command Description ls Lists contents of current directory ls -l Lists contents in list format cd Change current directory mkdir Make a new directory rm Remove a file rm -r Remove a directory cp file 1 file 2 Copies file 1 to file 2 cat file Prints file to the terminal wget url Downloads url to the current directory 7

Saint Louis University Editing Text Files ¢ Text files- very important! § C programs for this class § Very efficient storage for data and configuration ¢ Classic editors: vi and emacs § § ¢ Hard to get started initially Way faster once you get the hang of it Designed for low-bandwidth, spotty connections (think phone modems) Definitely worth it Other editors: § Text editors- search them! § GUI editors- search them! 8

Saint Louis University For next time: Find a good Linux environment you’d like to use ¢ Try logging into hopper. slu. edu ¢ Next homework involves writing C code ¢ 9

Saint Louis University Overview Linux ¢ C ¢ Hello program in C ¢ Compiling ¢ 10

Saint Louis University The C Language ¢ Developed at Bell Labs to write Unix § Practical language for practical projects § Most OSes are written mostly in C (some assembly code) § Most system libraries and tools are written entirely in C ¢ Small, simple language § Easy to learn (especially at the time) § Easy to port to different platforms ¢ Designed to replace Assembly Language § Provides low-level access to memory § Most operations map closely to assembly language operations ¢ Strongly typed, static type checking § int, unsigned, float, double, char, etc. § No runtime protection 11

Saint Louis University Type Checking in C ¢ Several primitive types: § int, unsigned, float, double, char, etc. ¢ ¢ The compiler will not warn about possibly unsafe operations: int a; unsigned b; b = a; Correctness is up to the programmer! § This kind of stuff is usually a bad idea though… 12

Command Line Input in C ¢ The main() function has two arguments: § argc is the number of arguments § argv is a vector of strings that hold those arguments E. g. : printing all values as strings int main ( int argc, char* argv[] ){ for( i = 0; i < argc; i++ ){ printf(“%sn”, argv[i]); } } 13

Converting Strings to Numbers ¢ How to convert “ 42” into the numeric value 42? ¢ atoi() § Fast, easy, but dirty § No safety or type checking § Undefined behavior on overflow ¢ scanf() § Works with floats and other data types § Undefined behavior on overflow ¢ strtol() § Robust error checking, industrial grade 14

Manual Pages! (A. K. A. man pages) All of C (and much more beside) is documented in the manual pages, use them! ¢ At the command prompt: man – manual for the manual pages() man atoi – manual for the function atoi() man scanf – manual page for the function scanf() ¢ ¢ Sometimes there are collisions: man printf – manual page for the bash command printf man 3 printf – manual page for the C function printf() man – shows man page sections 15

Saint Louis University C Operators ¢ Usual arithmetic operators: ¢ § +, -, *, %, /, = ¢ ¢ § && - logical AND § || - logical OR § ! - logical NOT Bitwise operators: § § § & - AND | - OR ^ - XOR ~ - complement << - left shift >> - right shift Ternary operator: Logical Operators: ¢ Relational Operators § § § == - True if equal != - True if not equal < - True if less than > - True if greater than <= - True if less or equal >= - True if greater or equal § (cond) ? (exec if true ) : (exec if false) 16

Hello, world! in C #include <stdio. h> int main( int argc, char* argv[] ){ int var = 42; printf(“Hello, world!n”); printf(“Value of var: %dn”, var); return 0; } 17

Compiling C programs ¢ We will use the gcc compiler ¢ If you have a program named prog. c: gcc -Wall -o prog. c § § -Wall turns on all warnings -o <name> output file name (default is a. out) Program files are listed by themselves Order isn’t important 18